Process as well as gas heater for heating a carrier gas stream

ABSTRACT

A gas heater ( 1 ) and gas heater method heat a carrier gas flow. The gas heater includes a gas inlet ( 2 ) a gas outlet ( 3 ) and a connecting gas channel ( 4 ). A heating system ( 5 ), arranged in the gas channel, includes a heat exchanger ( 12 ) surface. The carrier gas at least partly flows over the surface to heat the carrier gas flow. The gas channel includes a first section ( 6 ), arranged upstream of the heat exchanger in a flow direction, and a second section ( 7 ) arranged downstream of the heat exchanger. A respective sensor ( 8   a,    8   b ), for detecting a pressure value, is in the first and the second section or directly adjacent thereto. Pressure values are transmitted to a control and analysis unit ( 9 ) which ascertains a mass and/or volume flow of the carrier gas in the gas channel based on a pressure difference between the two pressure values.

CROSS REFERENCE TO RELATED APPLICATIONS

This application is a United States National Phase Application of International Application PCT/EP2017/000876, filed Jul. 19, 2017, and claims the benefit of priority under 35 U.S.C. § 119 of German Application 10 2016 008 952.0, filed Jul. 26, 2016, the entire contents of which are incorporated herein by reference.

TECHNICAL FIELD

The present invention pertains to a process as well as to a carrier gas heater, for heating a carrier gas stream, with a gas inlet and with a gas outlet which are connected by a gas duct. A heater, which releases heat to the carrier gas stream at least at times, is arranged in the gas duct between the gas inlet and the gas outlet in the flow direction of the carrier gas stream. The present invention further pertains to the use of a corresponding gas heater in a device for heating a carrier gas stream which is fed to a patient at least at times during anesthesia in order to supply the patient with an anesthetic as needed.

TECHNICAL BACKGROUND

A large number of anesthesia devices, with which an anesthetic is fed to a breathing gas stream for a patient for the temporary anesthetization of the patient ventilated by the anesthesia device during this period of time, are known from the state of the art. In this case, the temperature control of the carrier gas stream as well as the enrichment of the breathing gas stream with volatile anesthetic are of considerable importance, and the dispensing of an anesthetic as needed into the carrier gas stream especially depends on the accurate temperature control of the carrier gas stream, and especially on maintaining the necessary temperature. An excessively intensive cooling of the carrier gas stream is, above all, problematic since there is then a risk that not enough anesthetic evaporates. Anesthetic evaporators that operate mechanically for dispensing an anesthetic into a carrier gas stream and that are heated in a suitable manner by means of an electric heater have been known for many years.

The problem with mechanically adjustable anesthetic dispensers is that these require relatively large thermal storage masses, so that the device is prevented from cooling off when large evaporation mass flows are required, and then an inadmissible lowering of the vapor pressure and thus of the vapor output to be dispensed would occur. Mechanically operating anesthetic dispensers are often relatively heavy because of the required thermal storage masses, which in turn is disadvantageous for handling.

Based on the problems mentioned above, efforts have been made to replace mechanically adjustable anesthetic dispensers, which are relatively heavy especially because of the thermal storage masses, with electronically controlled anesthetic dispensers. In this connection, the temperature control of the carrier gas stream, to which the needed anesthetic shall be added, is of special importance.

In this connection, a device for dispensing an anesthetic into a carrier gas stream is known from DE 10 2014 008 625 A1, in which a novel evaporation principle is used. The technical solution being described is characterized in that the heat needed for the evaporation of the anesthetic located in the anesthetic evaporator is introduced into the evaporation chamber of the anesthetic dispenser with the carrier gas stream as needed. The introduction of the necessary heat into the carrier gas stream to be enriched with anesthetic takes place in this case as a function of the breathing gas volume flow needed for supplying the patient to be anesthetized as well as the anesthetic concentration in the gas stream. The heat output is set as a function of an anesthetic concentration/volume flow measured in the breathing system as well as corresponding set values predefined by the user.

SUMMARY

As the above explanations show, both the measurement of the breathing gas volume flow and the temperature of the carrier gas and the heating thereof are of special importance for the exact feeding of an anesthetic to a patient. Based on this problem, the basic object of the present invention is to provide a cost-effective, reliable and energy-efficient combination of a volume flow measurement with a carrier gas heating. A technical solution to be specified correspondingly shall be integrated here in a relatively simple manner in prior-art systems for the enrichment of a carrier gas stream with an anesthetic. Another, essential aspect of the present invention is that uncontrolled changes of the flow properties because of condensation, especially in the area of measurement points, are avoided in a reliable manner, wherein the heat needed for this or the heat output of a heating element shall at the same time be minimized.

The present invention pertains to a gas heater for heating a carrier gas stream with a gas inlet and with a gas outlet, which are connected by a gas duct. Carrier gas stream in the sense of the present invention is defined as a fluid stream, which contains air and/or at least one gas. Such a gas heater is thus capable of heating a gas, a mixture of at least two gases, a mixture of air and at least one gas or air. A heater with at least one heat exchanger, which heater releases heat to the carrier gas stream at least at times, is arranged in the gas duct between the gas inlet and the gas outlet in the flow direction of the carrier gas stream. The present invention is characterized in that the gas duct has at least one first section, which is arranged in the flow direction in front of the heat exchanger, as well as a second section, which is arranged in the flow direction behind the heat exchanger, that a sensor each is provided for detecting a pressure value in the first section and in the second section or directly adjacent hereto, and that the pressure values are sent to a control and analysis unit, which determines a mass flow and/or a volume flow of the carrier gas stream in the gas duct based on a pressure difference of the two pressure values.

The present invention is thus essentially characterized in that the heating of a carrier gas stream is combined with the detection of a mass flow and/or volume flow of the carrier gas stream, i.e., a so-called flow measurement, in one structural unit. The heating of a carrier gas stream as well as the measurement of a mass flow and/or volume flow can be carried out in this manner in an especially efficient and space-saving manner. The mass flow and/or volume flow is measured here according to the principle of pressure difference, which is currently usually also used in the area of anesthetic dispensing. The gas heater configured according to the present invention, which combines a heater with a device for measuring the mass flow and/or volume flow, can be used both for electronically controlled anesthetic dispensers and for mechanically adjustable evaporators, in which a volatile anesthetic is evaporated as needed and is absorbed by a carrier gas stream. After the set-up of a gas heater, measurements are preferably carried out, with which especially the flow resistance of the heater arranged between the pressure sensors in the gas duct is determined in case of different flow properties, i.e., in case of different volume flows and/or gas compositions. The recorded values are stored in the control and analysis unit of the gas heater or in a memory, which is set up to exchange data with the control and analysis unit unidirectionally or bidirectionally, and the values are used as a basis for the determination of the mass flow and/or volume flow carried out, taking into consideration the pressure difference prevailing between the two pressure sensors during the operation of the gas heater. The structural elements of the heater, especially the heat exchanger, arranged in the gas duct between the pressure sensors, quasi additionally assume the function of a measuring orifice for the determination of the mass flow or volume flow flowing through the gas heater during the operation of the gas heater. This illustrates the especially space-saving combination of a heater with a measuring element for the detection of a volume flow or mass flow in a gas heater.

The heater has a heating element which is supplied with energy from the outside and which is thermally coupled to the heat exchanger in a special embodiment of the present invention. The carrier gas stream flows at least partly over the heat exchanger surface of the heat exchanger in the operating state. The heating element is preferably a heating element supplied with electric energy, for example, a heating rod. It is also conceivable that the heating element is supplied with other heat-carrying media, for example, air, gas and/or vapor and the heat released by the heating element is finally released via the heat exchanger and here especially via the heat exchanger surface to the carrier gas stream. It is also conceivable that the heating element is a component, which releases heat through heat conduction or heat diffusion or conduction to the heat exchanger. Such a heat conduction is brought about by a temperature difference, and the heating element is supplied with heat from a heat source, which is arranged outside of the gas heater and this heat is sent to the heat exchanger based on the prevailing temperature gradient and from this heat exchanger to the carrier gas stream flowing through the gas heater.

Finally, the heating element may also be a radiation source, which heats the heat exchanger of the gas heater by heat radiation, especially IR radiation. Provisions are made according to a special embodiment of the present invention for the heating element and the heat exchanger, especially the heat exchanger surface, to be components of a structural element or to be integrated into a structural element.

It is always essential for the present invention that a heating element be provided, which releases its heat to a heat exchanger, which has a relatively large surface, so that the heat can be released over a large heat exchanger surface to the carrier gas stream. Provisions are made according to a special embodiment of the present invention for the heat exchanger to have ducts, ribs, open-pore structures or similar geometries, so that the transfer of heat to the carrier gas stream is carried out along a surface that is as large as possible.

According to a special variant, the heat exchanger is made of an open-pore, preferably sintered material. In this connection, a preferred variant is for the heat exchanger to be made of an open-pore, sintered metallic material or ceramic material. Such a metallic material or ceramic material may especially be a metallic foam or ceramic foam, for example, an aluminum foam.

The heat exchanger preferably has at least one recess, in which the heating element is arranged. It is conceivable in this case that the heat exchanger has a disk-like or cylindrical configuration in at least some parts and the heating element is arranged in a recess that is located in a disk or a cylinder of the heating element. A so-called sintered diaphragm or a sintered cylinder made of sintered material, especially made of sintered ceramic or sintered metal, is especially preferably used, in the interior of which is arranged a heating element, for example, in the form of a cylindrical cartridge-type heater, which is supplied with electrical energy for heating.

According to a special embodiment, a layer reflecting heat radiation is provided, which is arranged between the heat exchanger and a jacket element enclosing the heat exchanger in at least some areas. The heating element is thus preferably at least partially jacketed by the jacket element. In this case, it is, in principle, irrelevant whether such a jacket element is the outer housing of the gas heater itself or else a component wall enclosing the heat exchanger, which component wall is located in the interior of the gas heater. It is always essential for the layer reflecting heat radiation that the heat radiation originating from the heat exchanger be reflected effectively, so that, on the one hand, an energy-efficient heating of the carrier gas stream in the gas duct is guaranteed and, on the other hand, an inadmissible heating of the outer housing of the gas heater is avoided.

According to a very special embodiment, the jacket element is configured in the form of a tube, i.e., a jacket tube, in which the heat exchanger with the heating element located in it is arranged. The layer reflecting heat radiation, which reflects heat radiation originating from the heat exchanger in the direction of the heat exchanger, is preferably configured in the form of a film, which is applied to the outer surface of the heat exchanger and/or to a surface of the jacket element facing this heat exchanger. According to another alternative embodiment, the layer reflecting heat is configured in the form of a coating, which is applied to a surface of the jacket element facing the heat exchanger.

In a special embodiment of the present invention, at least one temperature sensor is arranged in the gas duct. The at least one temperature sensor is preferably arranged in the heat exchanger. The temperature values detected by the at least one temperature sensor are sent to a control and analysis unit, which can preferably actuate the heating element, taking the detected temperature values into consideration, and thus can influence the introduction of heat into the heat exchanger and finally into the carrier gas stream. Such a control and analysis unit is advantageously either connected to the central control unit of a device for dispensing anesthetic into the carrier gas stream or is part of such a control unit or is integrated into this control unit. It is ensured in this way that the heating element can be actuated in a targeted manner and the temperature of the carrier gas stream can be set at a needed value, taking into consideration the temperature detected in the gas duct of the gas heater and/or other measured values, which are recorded in the device for dispensing an anesthetic into a carrier gas stream, and/or set values, which are predefined by the user. Thus, for example, cooling effects, which are brought about because of the evaporation of an anesthetic in an anesthetic evaporator, can be offset precisely and rapidly in an especially reliable manner.

Furthermore, it is also conceivable to use the temperature values, which are detected by at least one temperature sensor and which are sent to a control and analysis unit, to determine a characteristic temperature, especially a temperature characteristic for the area of the transfer of heat from the heat exchanger to the carrier gas stream, which characteristic temperature is included in an algorithm for the temperature compensation of the pressure difference-volume flow measurement, on the basis of these detected temperature values. The often relevant temperature drifts of the materials, media and/or operating materials used, i.e., the temperature-dependent change in the physical properties of these materials, can be taken into consideration in this manner.

According to a very special variant of the present invention, at least two temperature sensors, which are each spaced apart from one another in the gas duct and which send the measured temperature values to a control and analysis unit, are provided, and a control signal is generated in the control and analysis unit for the operation of the heater based on a temperature difference between the at least two temperature values detected by different temperature sensors or taking into consideration a temperature gradient and/or a characteristic temperature value for the temperature compensation of the pressure difference-volume flow measurement.

At least one of the two pressure sensors provided in the gas heater is advantageously arranged in a flow-calmed area. Flow-calmed area in the sense of the present invention is considered to be an area in the gas duct or in the adjoining flow space, in which the gas located there flows relatively slowly or the flow even stops at least at times compared to the rest of the gas duct, and especially compared to the interior of the heat exchanger.

Moreover, the present invention pertains to a device for heating a carrier gas stream, which is fed to a patient at least at times during anesthesia, which has a gas heater, as it has been described above. Such a device is especially characterized in that the gas heater is arranged in the flow direction of the carrier gas stream in front of or behind an anesthetic dispenser, which adds an anesthetic to the carrier gas stream at least at times. The anesthetic dispenser is preferably an anesthetic evaporator, which adds a volatile anesthetic to the carrier gas stream by way of the evaporation principle, and the gas heater is fluidically connected in series with the anesthetic dispenser. The device configured according to the present invention thus contains a cost-effective, reliable and energy-efficient combination of flow measurement and carrier gas heating, which is especially advantageous for the anesthetic dispensing by means of electronically controlled dispensers. Here as well, the volume flow is measured on the basis of a pressure difference measurement, wherein it is reliably ensured by the technical solution according to the present invention that condensation is avoided in the area of the measured path. An essential advantage of the use of a gas heater configured according to the present invention in conjunction with an anesthetic dispenser is that the heat output needed for the as-needed heating of the carrier gas stream to be enriched with anesthetic is relatively low compared to prior-art heaters.

The present invention pertains, moreover, to a process for heating a carrier gas stream, in which a carrier gas stream is fed to a gas duct via a gas inlet and from which the carrier gas stream is released via a gas outlet. The carrier gas stream is heated at least at times by a heater arranged between the gas inlet and the gas outlet. The process configured according to the present invention is characterized in that a pressure value each is detected in the gas duct in a first section, which has a first flow cross section, as well as in a second section, which has a second flow cross section that is different from the first cross section, the pressure values are sent to a control and analysis unit, and a volume flow of the carrier gas in the gas duct is determined in the control and analysis unit based on a pressure difference of the two pressure values. According to a special variant of the process according to the present invention, at least one temperature is measured in the gas duct and/or in a component located in the gas duct or adjoining the gas duct. A control signal, on which are based the operation of the heater and/or a calculation of the volume flow prevailing in the gas duct on the basis of the detected pressure values, is preferably generated based on this detected temperature.

Provisions are made in a special variant of the present invention for the pressure measurements to be carried out in an area of the gas duct, in which the flow is calmed. For example, the pressure measurement is carried out in an area in front of or and/or behind the heat exchanger, which is thermally coupled to the heating element and through which the carrier gas stream flows. While a turbulent flow preferably prevails within the heat exchanger, a laminar flow prevails in the area, in which the pressure measurements are carried out, or the flow even stops at times.

The present invention will be explained in more detail below without limiting the general idea of the present invention on the basis of exemplary embodiments or reference to the figures. The various features of novelty which characterize the invention are pointed out with particularity in the claims annexed to and forming a part of this disclosure. For a better understanding of the invention, its operating advantages and specific objects attained by its uses, reference is made to the accompanying drawings and descriptive matter in which preferred embodiments of the invention are illustrated.

BRIEF DESCRIPTION OF THE DRAWINGS

In the drawings:

FIG. 1 is a schematic cross-sectional view of a gas heater with integrated pressure measurement points;

FIG. 2 is a schematic cross-sectional view of a gas heater with integrated pressure measurement points and temperature sensors;

FIG. 3 is a coaxially configured sintered gas heater with integrated pressure difference measurement and self-cooling housing;

FIG. 4 is a graphic diagram of the pressure loss curve in case of variable volume flow;

FIG. 5 is a graphic diagram of the heating of the carrier gas stream as a function of the heating time; and

FIG. 6 is a schematic sectional view of a gas heater.

DESCRIPTION OF PREFERRED EMBODIMENTS

Referring to the drawings, FIG. 1 shows a schematic cross-sectional view of a carrier gas heater 1 which is configured according to the present invention, and which has a carrier gas heater body with a gas inlet 2 and a gas outlet 3, which are connected to one another via a gas duct 4 defined by the carrier gas heater body. A rod-shaped heating element 11, which can be supplied with electric energy, and on which are arranged a plurality of disk-shaped sintered elements, forming a heat exchanger 12, is provided within the gas duct 4. The disk-shaped sintered elements have in their center a hole 13, so that the sintered disks can be pushed over the heating element 11 and can be in thermal contact with same. If the heating element 11 is supplied with electric energy, then this heating element is heated, and the heat is transferred to the sintered disks being used as heat exchanger 12.

The disks used in this exemplary embodiment are made of a sintered ceramic that has an open-pore structure, so that the surfaces of the disks are each connected to one another by small flow ducts. The open-pore structure is essential here, above all, so that other materials may also be used instead of a sintered ceramic. In this way, a heat exchanger 12 is provided, which has an especially large surface, along which the heat is transferred to the carrier gas stream.

The heating element 11 with the heat exchanger 12 fastened to it, which heat exchanger has a plurality of sintered disks, is enclosed by a jacket element 10. In the exemplary embodiment being shown in FIG. 1, the jacket element 10 is configured in the form of a jacket tube, into which the heating element 11 has been inserted together with the heat exchanger 12. A layer 15 reflecting infrared radiation is applied on the inside of the jacket element 10, which is configured as a tube, in order to be able to reflect the heat radiation originating from the heating element 11 as well as from the heat exchanger 12 into the gas duct 4 at least to a great extent. The layer 15 reflecting infrared radiation is in this case configured in the form of a film, which is applied to the inside of the jacket element 10 being used as jacket tube. It is also conceivable that a coating 15 reflecting infrared radiation is applied to the inner surface of the tube 10 in addition to or as an alternative to a film.

The gas heater 1 being shown in FIG. 1 has in its interior two sections 6, 7, which are arranged in the area of the gas duct 4 and between which is located a fluidic narrow space or constricted space, in the area of which a part of a heating element (11) as well as the heat exchanger (12) of the heater 5 are arranged. In the first section 6, which is arranged in the flow direction in front of the heat exchanger 12, and in the second section 7, which is arranged in the flow direction behind the heat exchanger 12, are arranged pressure measurement points 8 a, 8 b, respectively, at which the pressure prevailing in this area is detected and is sent to a control and analysis unit 9. A pressure difference is determined from the respective pressure value detected at a time and the volume flow of the carrier gas flowing through the gas duct 4 is calculated, taking the determined pressure difference into consideration. The increase in the flow rate at the constricted space brings about a reduction of the static pressure corresponding to Bernoulli's energy equation, so that there is a pressure difference between the two pressure measurement points 8 a, 8 b, which pressure difference is also called differential pressure and represents an indicator of the flow, i.e., the volume flow and/or mass flow, under known hydraulic conditions. The constricted space between the first section and the second section 7 of the gas duct 4 with the heat exchanger 12 of the heater 5 provided therein thus represents a type of measuring orifice, the flow resistance of which is used for determining the volume flow and/or mass flow. After the set-up of the gas heater, it has to carry out measurements only once in relation to its hydraulic properties, especially the flow resistance of the heat exchanger 12, and recorded values are stored in the control and analysis unit 9 or in a memory connected to same, so that these values can be taken into consideration in the determination of the volume flow or mass flow flowing through the gas heater 1 during the operation on the basis of the measured pressure difference.

As an alternative, it is conceivable that other pressure sensors 8, for example, a Pitot tube or Prandtl probe, are also used for determining the pressure difference between the two pressure measurement points 8 a, 8 b. These sensors take into consideration the energy conservation law in the form set up by Bernoulli. In this case, it is taken into consideration that the kinetic energy of the carrier gas stream can be converted. If a change in the flow cross section occurs, this means that the flow rate of the flowing fluid and thus also the pressure change. The pressure prevailing in the fluid as well as the flow rate are thus directly related.

The gas heater 1 being shown in FIG. 1 has, furthermore, a housing 14, in which are arranged the gas duct 4 with the pressure measurement points 8 a, 8 b as well as the heating element 11 with the heat exchanger 12, which represent the principal components of the heater 5 of the gas heater 1. An insulation or thermal insulation 16, which counteracts an inadmissible heating of the housing 14, is provided in the area between the housing 14 and the heat exchanger 12 with the heating element 11 arranged in it. Since a small gap 19, in which a partial stream of the carrier gas flows from the gas inlet 2 to the gas outlet 3, without flowing through the heat exchanger 12, preferably remains between the heat exchanger 12 and the jacket tube 10 enclosing same, a further cooling between the heat exchanger 12 and the housing 14 is achieved. An inadmissible heating of the jacket tube 10 is reliably counteracted by this feature. The radial temperature gradient developing within the carrier gas stream in this connection, namely the temperature difference between the carrier gas stream in the interior of the heat exchanger 12 and the carrier gas stream in the area of the gap 19 between the heat exchanger 12 and the jacket tube 10 is knowingly accepted.

According to FIG. 1, a slim, electric cartridge-type heater as heating element 11 is thus inserted into a heat exchanger 12, which is manufactured from a plurality of cylindrical diaphragms that are made of a sintered ceramic material, and the gas heater 1 thus formed is combined with a volume flow measurement.

The heat output of the electric cartridge-type heater 11 used is in a range of up to 30 W. The pressure measurement connections 8 a, b are each located in a flow-calmed area 18, 20 in front of and behind the heat exchanger 12, respectively, so that a reliable pressure measurement is made possible. Inadmissible heating is prevented by the carrier gas to be heated flowing by in the direct vicinity of the jacket tube 10 on the inside of same in the gap 19 provided for this. It is, moreover, possible due to the integrated flow measurement to operate the heater 5 in proportion to the respective determined flow.

Further, a characteristic temperature, which is included in an algorithm for the temperature compensation of the pressure difference-volume flow measurement, is determined in the sintered ceramic heat exchanger 12 by means of suitable temperature sensors 17 a, 17 b. In this manner, the relevant temperature drifts of the substance data of the materials being used in the gas heater 1 are offset. As can be seen in FIG. 1, two temperature sensors 17 a, 17 b, which are arranged spaced apart from one another within the heat exchanger 12, are provided according to this exemplary embodiment. According to the exemplary embodiment shown in FIG. 1, the two temperature sensors 17 a, 17 b are each arranged behind one another in the flow direction in different disks of the heat exchanger 12.

Complementary to FIG. 1, FIG. 2 likewise shows a cross-sectional view of a gas heater 1, in which a volume flow measurement is carried out by means of two pressure sensors 8 a, 8 b. In this case as well, the gas duct 4, which extends from a gas inlet 2 up to a gas outlet 3 of the gas heater 1, has two sections 6, 7, between which is located a narrow space or constricted space with a heat exchanger 12 arranged in this area. In each of these areas 6, 7 is located a pressure measurement point each, in which the static pressure prevailing in the flowing carrier gas is detected by means of a pressure sensor 8 a, 8 b and is sent to a central control unit 9.

A heat exchanger 12, which has a disk-shaped or cylindrical configuration, is in turn arranged in the interior of the gas duct 4. This heat exchanger 12 is heated by means of an electrical heating element 11, which is fastened to the heat exchanger 12 within same, so that a carrier gas flowing through the gas heater 1 absorbs heat from this heat exchanger during the flow through the heat exchanger 12. Within the gas duct are provided three points, at which the temperature prevailing in this area is detected by means of temperature sensors 17 a, 17 b, 17 c, respectively. The three temperatures are likewise sent to a control and analysis unit 9. A characteristic temperature for the heat exchanger 12, on which are based the actuation of the heating element 11 and/or the calculation of a volume flow value, is calculated by means of the control and analysis unit 9 on the basis of the determined three temperatures. It is of special importance here that the substance data, which are respectively relevant for the heat conduction, especially the heat-conducting components, can be taken into consideration in the determination of the volume flow based on the determined temperatures or the temperature gradient prevailing in the area of the heat exchanger 12.

FIG. 3 likewise shows a sectional view of a gas heater 1 configured according to the present invention, in which a volume flow determination of the carrier gas stream flowing through the gas heater 1 is carried out. Especially the individual components of the gas heater 1 can be seen here in FIG. 3. The heat exchanger 12, which has an open-pore structure, is configured in the form of a cylinder. A hole, into which is inserted a heating element 11, which is supplied with electric energy, is provided as a recess 13 in the interior of the cylinder. The heat exchanger 12 with the heating element 11 arranged in it is enclosed by a jacket element 10, which is configured as a tube.

The flow path of the gas heater 1 is formed by a gas inlet 2 and a gas outlet 3 as well as a gas duct 4 connecting the gas inlet and the gas outlet 2, 3. After the carrier gas stream flows into the gas heater 1 through the gas inlet 2, the carrier gas flows through the heat exchanger 12, is heated here and finally flows out of the gas heater 1 again through the gas outlet 3.

On its side facing the gas inlet 2, the jacket tube 10 is attached to a connection surface of a sealing disk 21, the jacket tube 10 is being positioned and clamped between this disk 21 and a conical spring 22. A washer 24, which assumes essentially two functions, is provided between the conical spring 22 and the jacket tube 10. On the one hand, the conical spring 22 is centered in relation to the jacket element 10 by means of the washer 24 and the contact pressure originating from the spring 22 is evenly transferred to the jacket tube 10 and, on the other hand, the heat exchanger 12, here in the form of filaments, is fixed in its position.

The sealing disk 21, which has a circular-ring-shaped inlet opening 23 for the flowing carrier gas stream, is inserted or pressed into the housing 14 with a slight interference fit on its circumferential surface. It is ensured in this manner that the carrier gas stream into the gas heater 1 fully reaches the jacket tube 10, in which the heat exchanger 12 with the heating element 11 is located.

The sealing of the housing 14 of the gas heater is brought about by means of a housing cover 25, which has a two-part configuration and is sealed via O-rings against the housing 14 as well as against the heating element 11, which passes through the housing cover 25.

In order to limit heat losses, a polyimide film 15, which prevents a contact between the hot carrier gas and the jacket tube 10 and furthermore with the housing 14, is provided on the inner side of the jacket tube 10. This film 15 reflects infrared radiation at least to a great extent, so that the infrared radiation coming out of the direction of the heating element 11 as well as of the heat exchanger 12 is again reflected back in the direction of the heat exchanger 12. The polyimide film 15 jackets the heat exchanger 12 and is clamped on the side facing the gas inlet 2 between the sealing disk 21 and the jacket tube 10. The polyimide film is arranged on the side facing the gas outlet 3 and is configured in the form of a funnel, which passes over into a hollow cylinder, such that the carrier gas flowing out of the heat exchanger 12 and the jacket tube 10 within the film 15 leaves the gas heater 1 via the gas outlet 3.

Further, an insulating material 16, especially an insulating fibrous material, which contains ceramic wool in this case, is provided between the jacket tube 10 and the housing 14 of the gas heater 1. This insulation counteracts a heat conduction from the jacket tube 10 onto the housing 14 at least to a considerable extent.

Pressure sensors 8 a, 8 b, which detect the pressure in the carrier gas in comparatively flow-calmed areas 18, 20 and send same to a control and analysis unit 9, are each arranged in these areas 18, 20 both in the first section 6 in front of the heat exchanger 12 and in the second section 7 behind the heat exchanger 12. A pressure difference is determined in the control and analysis unit 9 on the basis of the detected pressure values and from this a volume flow of the carrier gas flowing through the gas heater 1 is determined according to the rules of the pressure difference method. Because of the heating of the gas duct 4, the carrier gas can, on the one hand, be heated to a temperature needed for the use of the carrier gas for a further process, for example, for the enrichment with anesthetic, and, on the other hand, it is ensured that condensation effects, which would interfere with the determination of the volume flow in the interior of the gas heater 1, are largely ruled out.

Furthermore, temperature sensors 17 a, 17 b, which detect the respective temperature in this area and likewise send same to the control and analysis unit 9, are provided at different points of the heat exchanger 12. A temperature difference or temperature gradient is determined from the determined temperatures, so that a characteristic temperature can finally be determined for the heat exchanger 12, which is included in an algorithm for the temperature compensation of the pressure difference-volume flow measurement. The relevant temperature drifts of the substance data of the components involved in heat conduction are herewith taken into consideration and can be offset by means of suitable actuation of the heating element 11.

Condensation in the area of the gas heater 1, especially at the pressure sensors 8 a, is avoided with certainty by means of the technical solution described. Furthermore, the heat output necessary for the heating is limited to an economically significant extent. A characteristic gas temperature for calculating the volume flow and for monitoring the heating element 11 can be determined and the carrier gas stream can be heated in an energy-efficient and reliable manner with a moderate drop in pressure and with relative low excess temperatures. The drop in pressure between the two pressure sensors 8 a, 8 b is about 30 mbar at a volume flow of 5 L/min during the normal operation.

FIG. 4 shows for this the measured values recorded with a prototype of a gas heater 1. The volume flow of a carrier gas stream, here an air stream, flowing through the gas heater 1 is plotted on the X axis in a range of 0 L/min to 8 L/min, while the pressure difference between the two pressure sensors 8 a, 8 b is plotted on the Y axis in a range of 0 mbar to 60 mbar.

A gas heater 1 configured according to the present invention can preferably be used in connection with anesthetic dispensers, as they are used in modern anesthesia apparatuses. A carrier gas stream, which is fed to the anesthetic dispenser, especially to an anesthetic evaporator, can be heated by means of such a gas heater 1 to the required temperature and at the same time the mass flow and/or volume flow of the carrier gas stream flowing through the gas heater can be determined. The gas heater is preferably arranged in the flow direction of the carrier gas in front of the anesthetic evaporator. In principle, however, it is also conceivable to arrange a correspondingly configured gas heater in the flow direction downstream of the anesthetic dispenser as a function of carrying out the anesthetic dispensing.

Since not only the temperature of the carrier gas stream, but also the volume flow thereof is of decisive importance for the enrichment of a carrier gas stream with a quantity of anesthetic needed for the anesthetization of the patient, a gas heater 1 configured according to the present invention represents a component which can be used in an especially advantageous manner, because both a heating of the carrier gas and the determination of the volume flow can be achieved in a highly precise and yet energy-efficient manner. Compared to conventional anesthetic dispensers, which often have external heat sources and relatively large thermal masses to prevent an inadmissible cooling of the anesthetic dispenser, the above-described gas heater, which is integrated into the gas circuit, requires a relatively low heat output in order to heat up the carrier gas stream to the needed temperature and to reliably counteract a cooling of the anesthetic evaporator, which cooling occurs in case of removal of a large quantity of vapor.

In this connection, FIG. 5 shows a graphic diagram of values, as they were again recorded with the prototype of a gas heater. In this case, a carrier gas stream with a volume flow of 8 L/min flowed through the gas heater used. The maximum heat output of the heating element used was 30 W. After 28 sec, the output was reduced and was only 17.2 W to 17.7 W for the remaining time of the test shown in FIG. 5.

A time period of 0 min to 7 min is plotted on the X axis in the diagram shown in FIG. 5. The values plotted on the Y axis correspond to temperatures in a range of 0° C. to 160° C. The function curve T₂ shows the temperature of the housing of the gas heater 1 over the plotted time period of 0 min to 7 min. As can be seen, the temperature T₂ of the housing increases only by about 17 K, namely from 22° C. to 39° C. because of the film reflecting infrared radiation provided in the interior, because of the cooling gap and because of the thermal insulation additionally provided between the jacket element and the housing. Contact with the housing is thus possible without problems, especially without this being connected with risks for the user.

The function curve T₁ represents the temperature of the carrier gas stream at the gas outlet 3, and air was used as the carrier gas in the test in question here. The temperature value increases to 120° C. at first within about 28 sec and remains approximately constant at a value of 105° C. over the next 6.5 min. In this case as well, the decrease in the temperature after 5 min can be attributed to a change in the volume flow from 0.00775 m³/min to 0.008 m³/min.

It is essential, above all, at the temperature curves T₁, T₂ shown in FIG. 5 that a carrier gas temperature T₁ be already reached at the gas outlet 3 after about 30 sec despite relatively low heat output, which temperature continues to remain almost constant.

A cylindrical cartridge-type heater was used as the heating element (T+H 0214 HLP (d5; L60; 100 W; 24 V), which is thermally coupled to the heat exchanger, which consisted on five disks made of porous aluminum with a pore diameter of 200 m to 250 m.

Further, FIG. 6 shows a schematic sectional view of a gas heater 1 configured according to the present invention, wherein the sectional plane is arranged at right angles to the main direction of extension of the gas heater and thus to the main direction of flow of the carrier gas. An essential feature of the embodiment being shown is that the gas inlet 2 and especially the inflow direction is arranged in parallel and at a vertical distance to the center line running from top to bottom in the drawing plane. It is ensured in this manner that the carrier gas flowing in can flow evenly along the circumference in the inflow section. Finally, a flow develops, which is directed in a funnel-shaped manner towards the inlet of the heat exchanger or towards the inlet opening shown in FIG. 3 in the sealing disk 21. The pressure measurement point for the first pressure sensor 8 a, viewed in the flow direction, can be seen on the side of the center line located opposite the gas inlet.

It is essential for the described solution according to the present invention that a gas heater be provided, with which a volume flow of the carrier gas can be determined simultaneously with the heating of a carrier gas stream, wherein both the heating and the determination of the volume flow are achieved in a highly precise and energy-efficient manner.

While specific embodiments of the invention have been shown and described in detail to illustrate the application of the principles of the invention, it will be understood that the invention may be embodied otherwise without departing from such principles. 

1. A carrier gas heater for heating a carrier gas stream, the gas heater comprising: a gas duct with a gas inlet and with a gas outlet, which are connected by the gas duct; a heater arranged in the gas duct at least partly between the gas inlet and the gas outlet in a flow direction of the carrier gas stream, the heater comprising a heat exchanger with a heat exchanger surface which the carrier gas stream flows over at least partly in an operating state, so that the heat exchanger at least at times releases heat to the carrier gas stream, wherein the gas duct comprises at least one first section arranged in the flow direction in front of the heat exchanger and a second section arranged in the flow direction behind the heat exchanger; a first sensor provided for detecting a pressure value in the first section or directly adjacent hereto; a second sensor provided for detecting a pressure value in the second section or directly adjacent hereto; and a control and analysis unit wherein the detected pressure values are sent to the control and analysis unit and the control and analysis unit is configured to determine a mass flow and/or volume flow of the carrier gas stream in the gas duct based on a pressure difference of the detected pressure values.
 2. A carrier gas heater in accordance with claim 1, wherein the heater further comprises a heating element and the heat exchanger is thermally coupled to the heating element, which is supplied with energy from outside of the carrier gas heater.
 3. A carrier gas heater in accordance with claim 2, wherein the heat exchanger and the heating element form a structural unit.
 4. A carrier gas heater in accordance with claim 1, wherein the heat exchanger is made of a sintered material.
 5. A carrier gas heater in accordance with claim 1, wherein the heat exchanger is made of an open-pore metallic material or ceramic material.
 6. A carrier gas heater in accordance with claim 1, wherein the heat exchanger has a recess (13), in which the heating element is arranged.
 7. A carrier gas heater in accordance with claim 1, further comprising: a housing, which encloses the gas duct in at least some areas; and a layer, reflecting heat radiation, arranged between the housing and the heat exchanger.
 8. A carrier gas heater in accordance with claim 7, wherein the layer reflecting heat radiation is configured as an insulating film.
 9. A carrier gas heater in accordance with claim 1, further comprising at least one temperature sensor arranged in the gas duct.
 10. A carrier gas heater in accordance with claim 9, wherein the at least one temperature sensor is arranged in the area of the heat exchanger.
 11. A carrier gas heater in accordance with claim 1, further comprising temperature sensors spaced apart from one another in operative connection with the gas duct, wherein each of the temperature sensors sends measured temperature values to the control and analysis unit wherein a control signal for operation of the heater is generated in the control and analysis unit based on a temperature difference between the two temperature values detected by the two temperature sensors.
 12. A carrier gas heater in accordance with claim 1, wherein data in relation to at least one hydraulic property of the heat exchanger, which is arranged between the first section and the second section of the gas duct, are stored in the control and analysis unit and/or in a memory communicating with the control and analysis unit.
 13. A device for heating a carrier gas stream, which is fed to a patient during anesthesia at least at times, the device comprising a gas heater, the heater comprising: a gas duct with a gas inlet and with a gas outlet, which are connected by the gas duct; a heater arranged in the gas duct at least partly between the gas inlet and the gas outlet in a flow direction of the carrier gas stream, the heater comprising a heat exchanger with a heat exchanger surface which the carrier gas stream flows over at least partly in an operating state, so that the heat exchanger at least at times releases heat to the carrier gas stream, wherein the gas duct comprises at least one first section arranged in the flow direction in front of the heat exchanger and a second section arranged in the flow direction behind the heat exchanger; a first sensor provided for detecting a pressure value in the first section or directly adjacent hereto; a second sensor provided for detecting a pressure value in the second section or directly adjacent hereto; and a control and analysis unit wherein the detected pressure values are sent to the control and analysis unit and the control and analysis unit is configured to determine a mass flow and/or volume flow of the carrier gas stream in the gas duct based on a pressure difference of the detected pressure values, wherein the gas heater is arranged in the flow direction of the carrier gas stream in front of or behind an anesthetic dispenser, which adds at least one anesthetic to the carrier gas stream.
 14. A process for heating a carrier gas stream, the process comprising the steps of: feeding a carrier gas stream to a gas duct via a gas inlet and releasing the carrier gas stream from the gas duct via a gas outlet; heating the carrier gas stream between the gas inlet and the gas outlet at least at times by a heater, which has a heat exchanger, over a heat exchanger surface of which the carrier gas stream flows at least partly in the operating state; detecting a pressure value in the gas duct in a first section arranged in the flow direction in front of the heat exchanger as well as in a second section arranged behind the heat exchanger; sending the detected pressure values to a control and analysis unit; and determining a mass flow and/or volume flow of the carrier gas in the gas duct in the control and analysis unit based on a pressure difference of the two pressure values.
 15. A process in accordance with claim 14, wherein at least one temperature is measured in the gas duct and/or in a component located in the gas duct or adjoining the gas duct.
 16. A process in accordance with claim 15, wherein a control signal, on which the operation of the heater is based, is generated based on the detected temperature. 